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Navien E016 — Heat Exchanger Overheating
Your Navien shut down because the heat exchanger ran past its safe temperature limit — almost always a scale or water-flow problem, not a gas problem.
$99 dispatch and diagnosis fee — waived if you approve the repair
The E016 lockout means the temperature inside the heat exchanger climbed past the point Navien considers safe. When water can't carry heat away from the exchanger fast enough, the metal temperature spikes and the unit shuts itself down to protect the heat exchanger from damage.
The good news: E016 is almost never a combustion or gas fault. It's a flow-and-scale story. The fix is usually restoring proper water flow and descaling the heat exchanger — routine maintenance that also keeps the code from coming back.
What causes E016
1. Scale buildup in the heat exchanger
Hard water leaves mineral scale that insulates the heat exchanger and chokes flow. The most common root cause on units that have never been descaled. A flush usually clears it.
2. Restricted or low water flow
A partially closed valve, low incoming pressure, or a clogged fixture can drop flow below what the unit needs to shed heat, tripping the over-temp limit.
3. Clogged cold-water inlet filter
Navien units have an inlet screen that traps debris. When it clogs, flow through the exchanger drops and temperatures climb. A quick clean often resolves it.
4. Failed high-limit sensor
Less common, but a faulty over-temperature sensor can report a false high reading. We verify the sensor before condemning anything expensive.
What you can safely check first
- Check that the cold-water inlet filter is clean and every supply valve is fully open.
- One reset is reasonable: power the unit off at the disconnect, wait 30 seconds, and power it back on.
- If E016 returns after that, stop resetting. Restarting an overheating unit only delays the descale it is asking for.
When to stop and call us
A heat exchanger that keeps overheating needs a professional descale and a flow check, and the high-limit sensor has to be verified before anything expensive is condemned. Both are routine, and both need a licensed technician.
Need Navien repair on the South Shore?
An error-code guide can explain the symptom. If your home is in Hull, Quincy or our surrounding South Shore service area, Johnson Bros. can help with the next step: diagnosing your Navien boiler, combi boiler or tankless water heater.
The house has no heat
Tell us whether every room is cold or just one heating zone, and whether the boiler display shows a code.
Boiler and no-heat repairThe taps have no hot water
Check whether it affects one fixture or every hot tap. Tell us if you have a tank, a tankless heater, or a boiler that also heats your water.
Help with no hot waterBoth stopped working
Mention both symptoms when you call, especially with a combi boiler. Have the brand, model and displayed code ready if you can read them safely.
Navien service and repairCalls are answered 24/7. Call for urgent no-heat or no-hot-water trouble; we will confirm appointment availability. Online booking does not guarantee immediate dispatch.
Local service: Hull heating repair · Quincy · Weymouth · Hingham · Braintree · Abington.
Smell gas? Leave the house first, then call the gas utility or 911 from outside. Do not use switches, phones or anything that sparks inside the building, and do not go looking for the source. Call us afterwards, once it is safe, for the repair.
Seeing E016 on your Navien?
Book online and we will diagnose the actual cause, explain what we find, and price the repair before starting.
Navien E016 FAQs
What does Navien error code E016 mean?
E016 is a heat-exchanger overheat lockout. The unit detected the heat exchanger running hotter than its safety limit and shut down to protect itself. It's a protective response — but it needs to be addressed so it doesn't keep recurring.
What causes E016?
Most often scale buildup inside the heat exchanger or reduced water flow — a clogged inlet filter, a partially closed valve, or low incoming pressure. Hard-water scale is the number-one culprit on units that have gone years without a descale. Occasionally it is a faulty high-limit sensor.
Can I fix E016 myself?
You can safely try one reset — power the unit off at the disconnect, wait 30 seconds, and power it back on — and check that the cold-water inlet filter is clean and all supply valves are fully open. If it clears and stays clear, great. If E016 comes back, the heat exchanger likely needs a professional descale. Repeatedly resetting an overheating unit just delays the real fix.
How much does E016 repair cost?
The $99 service fee sends a licensed technician out to diagnose the problem. Approve the repair on the spot and the fee is not charged at all; decline it and the $99 covers the visit. Most E016s are resolved with a descale/flush and a flow check rather than parts, which keeps the cost predictable. If a sensor is at fault, it is a modest part.
Other codes on this unit? See all Navien error codes.
Why South Shore homeowners choose Johnson Bros.
Navien E016 diagnosed properly
We diagnose the cause rather than clearing the code and hoping. You get an upfront price before any work starts.
Not sure what's wrong? Send a photo or videoBooking online is the quickest way to hold the next open appointment. Call instead if it is urgent and you would rather talk to someone.
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Related services
All Navien error codes
The other codes this unit can show, and what each one means.
Navien service and repair
Installation, service and repair for Navien equipment on the South Shore.
Water heater repair and replacement
Repair and replacement options for tank and tankless water heaters.
Family Plan
Members get 10% off, priority scheduling, and the $99 fee waived even if you decline the quote.
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Navien E016 diagnosed properly
We diagnose the cause rather than clearing the code and hoping. You get an upfront price before any work starts.
Call for urgent help now. Book online when you want the next available fit for your schedule.